Information on the consumption of food items from plants of C3 and C4
photosynthetic cycle by a bird community can help determine the potential resilience
of forest remnants in agricultural landscapes. This study assessed the diet
composition of bird communities in forest fragments embedded in the agricultural
landscape of the Corumbataí River basin, São Paulo State, Brazil, using stable
isotopes. Eight forest fragments were selected based on their ages, being four
classified as “old” (33 and 49 years of age) and four “young” (3 to 11 years of age),
arranged in equal proportion in sample units (16 km2), with at least 70% of
occupation by the matrix (pasture or sugarcane) and 10% of forest. We performed 12
repetitions in each remnant, totaling 96 sampling. A sequence of five ornithological
mist nets (32 mm mesh, 12 m x 2.8 m) was allocated in the nuclear area of each
remnant, remaining open for a continuous period of four hours, in the early morning
hours. The nets were inspected every 30 minutes. Feather samples were collected
for isotopic analysis. We analyzed isotopically 33 species. The percentage of C3
found in individuals of 11 species was related to landscape metrics (percentage of
sugarcane and pasture and percentage of forest or nuclear area, mean annual forest
change rate, forest change curvature profile and average age). We identified 81
species belonging to 27 families in 979 catches. The most frequently captured
species were B. hypoleucus (84.38%), A. galeata (83.33%) and P. mystaceus
(71.88%). There was no statistical difference for predominance between the
communities in pasture and sugarcane or between old and young remnants. The
similarity between the communities in pasture and sugarcane matrices was 50.62%,
and 48.15% comparing old and young forest remnants. The isotope analysis of 33
species showed differences in the use of plant resources of C3 and C4 photosynthetic
cycle. A total of 78.79% of species had a diet average over 70% of its food
consumption solely based on C3 plants, 21.21% consumed C3 and C4 and no species
showed predominant consumption of C4 plants. Individual analysis, however, showed
that T. fuliginosus and B. flaveolus predominantly consumed C4 plants. Among the 11
species studied, six (A. galeata, A. flavirostris, B. flaveolus, L. euleri, T. coronatus
and T. leucomelas) showed a relationship with the landscape variables tested. Diet
composition of species was mainly affected by the remnant average age, and results
were different regarding the type and ratio of the landscape matrix. Although the
fragments sampled are in advanced stage of degradation, the results corroborate the
need to preserve these remnants to maintain biodiversity of birds.
